How are RFID antennas designed?
RFID uses inductive near-field coupling at LF (125–134 kHz) and HF (13.56 MHz), and radiative backscatter at UHF (860–960 MHz, regionally 902–928 MHz in the US and 865–868 MHz in Europe).[1][2] UHF passive tag antennas are dipole-like structures conjugate-matched to the capacitive chip impedance, often with a T-match; read range follows from a Friis-based formula that includes the chip’s power threshold.[3]
How is UHF tag read range estimated?
Rao, Nikitin and Lam give r = (λ/4π)·√(PtGtGrτ/Pth), where Pth is the chip’s minimum power and τ = 4RcRa/|Zc+Za|² the power transmission coefficient between chip and antenna.[3] Range is usually forward-link (tag power) limited.
Why conjugate match instead of 50 Ω?
The chip input is a small resistance in series with a large capacitive reactance. The antenna is designed with an inductive impedance equal to the conjugate, using a T-match or inductive loop, so maximum power reaches the rectifier.[3]
How do LF and HF RFID antennas differ?
At LF and HF, wavelengths (about 2.3 km at 130 kHz and 22 m at 13.56 MHz) are huge compared with tags, so tags and readers use resonant coils coupled by mutual inductance. Range is roughly limited to a fraction of the reader coil diameter, typically centimeters to about a meter for vicinity cards.[1]
Frequently asked questions
Why do metal and liquids degrade UHF tags?
They detune and shield dipole-like tags; on-metal tags use patch-like designs with a ground.
Is circular polarization used for RFID readers?
Yes; it reads randomly oriented linear tags at a 3 dB cost.
What standard governs UHF RFID?
EPC UHF Gen2, also ISO/IEC 18000-63.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “RFID Handbook, 3rd ed.”. K. Finkenzeller, Wiley. 2010.
- “EPC UHF Gen2 Air Interface Protocol (also ISO/IEC 18000-63)”. GS1. current version.
- “Antenna Design for UHF RFID Tags: A Review and a Practical Application”. K. V. S. Rao, P. V. Nikitin and S. F. Lam, IEEE Transactions on Antennas and Propagation, vol. 53, no. 12, pp. 3870-3876. December 2005.